Falling film heat exchangers usually include an array of vertical tubes. The tubes can be exposed or surrounded by a shell. The process liquid can be either inside or outside the tube with the heat exchange fluid on the other side.
Although falling film heat exchangers are often used to heat a liquid feed stream, they can be used for cooling such a stream. Falling film heat exchangers of the described types can be used as freeze exchangers for producing fresh water from brackish water and seawater, for concentrating fruit and vegetable juices, and industrial crystallization processes. See U.S. Pat. No. 4,286,436. As the liquid flows through each tube, it can be cooled enough to crystallize a solid from the liquid. Thus, by cooling seawater, ice is obtained which when separated, washed and melted provides potable water. When a fruit or vegetable juice is similarly chilled, ice forms and is removed to provide a concentrated juice.
Freeze exchangers of the described type can use any cooling fluid to cool a liquid flowing downwardly on the tubes. Some suitable cooling fluids are refrigerant gases such as ammonia and Freon brand refrigerants.
Whether the heat exchanger is used to heat or cool a process or feed liquid, it is desirable to be able to control the thickness and uniformity of the falling film on each tube. Generally, acceptable results are not obtained by simply supplying enough liquid to flow down each tube because the feed to each tube is most often nonuniform, with some tubes receiving much more, and others much less, liquid than desired for optimum heat exchange results. There is a need, accordingly, for apparatus which will facilitate supplying the refrigerant and/or process or feed liquid to the tubes to produce falling films uniformly thick and evenly distributed on the surface of each tube.